Coronary artery disease (CAD) is the most common form of heart disease, affecting millions of people. Peripheral artery disease (PAD) also affects millions of people. CAD and PAD most often results from a condition known as atherosclerosis, which generally manifests as the accumulation of a waxy substance on the inside of a subject's arteries. This substance, called plaque, is made of cholesterol, fatty compounds, calcium, and a blood-clotting material called fibrin.
As the plaque builds up, the coronary and peripheral arteries narrows, or becomes stenotic, making it more difficult for blood to flow to the heart. As the blockage worsens in a person's coronary arteries, blood flow to the heart slows, and a condition called angina pectoris, or simply angina, may develop. Angina is like a squeezing, suffocating, or burning feeling in the chest. The pain typically develops when the heart requires additional blood, such as during exercise or times of emotional stress. In time, a narrowed or blocked artery can lead to a heart attack. A number of medicines can be used to relieve the angina pain that comes with CAD, but these medicines cannot clear blocked arteries. A moderate to severely narrowed coronary artery may need more aggressive treatment to reduce the risk of a heart attack. As the plaque builds up in peripheral arteries, the artery narrows, or becomes stenotic, thereby making it more difficult for blood to flow through the peripheral arteries. The reduced blood flow in the peripheral arties limits the amount of oxygen that is delivered to the extremities, which in turn may cause pain in the extremities and, in severe cases, gangrene, which may ultimately require amputation.
Balloon angioplasty and other transluminal medical treatments are well-known and have been proven efficacious in the treatment of stenotic lesions at the core of CAD and/or PAD. In a typical angioplasty procedure, a catheter is inserted into the groin or arm of a subject and guided to the affected arteries, such as the aorta and into the coronary arteries of the heart when treating CAD and the peripheral arteries when treating PAD. There, blocked arteries can be opened with a balloon positioned at the tip of the catheter. Initially, angioplasty was performed only with balloon catheters, but technical advances have been made and improved patient outcomes have been achieved with the placement of small metallic spring-like devices called “stents” at the site of the blockage. The implanted stent serves as a scaffold that keeps the artery open. Angioplasty and stenting techniques are widely used around the world and provide an alternative option to bypass surgery for improving blood flow to the heart muscle. There are, however, limitations associated with angioplasty and stenting, one of which is called “restenosis.”
Restenosis occurs when the treated vessel becomes blocked again. For example, when a stent is placed in a blood vessel, new tissue grows inside the stent, covering the struts of the stent. Initially, this new tissue consists of healthy cells from the lining of the arterial wall (such as, endothelium). This is a favorable effect because development of normal lining over the stent allows blood to flow smoothly over the stented area without clotting. Later, scar tissue may form underneath the new healthy lining. However, in about 25 percent of patients, the growth of scar tissue underneath the lining of the artery may be so thick that it can obstruct the blood flow and produce another blockage. “In-stent” restenosis is typically seen 3 to 6 months after the initial procedure. Another significant limitation of the use of stents is stent thrombosis, which, although rare (occurring in only 1 percent of patients), most commonly presents as acute myocardial infarction.
In addition to angioplasty and the deployment of stents, other types of intervention for stenotic vessels include atherectomy, bypass surgery, and the use of laser ablation and mechanical cutting systems to reduce the plaque size. Treatments using various pharmacological agents have also been developed, including medical infusions, drug-eluding stents (DES), and drug eluting balloons (DEB). Given the persistence of CAD and PAD, however, the most efficacious means for improving therapeutic outcomes may involve combinations of therapies designed not only to reduce plaque size in the short term, but also to prevent future complications such as restenosis. Combinatorial therapies may offer the best chance to improve therapeutic outcomes for people suffering from CAD and PAD.